I modified the given echo client to a echo client in multi user chat (MUC).
The following requirements are necessary for the MUC:
- 'Members only'
- 'Moderated' (only members can send messages)
- 'real JID' has to be visible to anyone for receiving the members' OMEMO key.
The bot tries always to answer encrypted, because sometimes the inital publish of the own OMEMO key does not seem to be regocnised by some client.